I. Field of The Invention
This invention relates to a mechanical jack for raising and lowering an object such as a trailer and, in particular, to a gear drive for the jack which can be readily assembled within the jack tube and, if necessary disassembled for repair or replacement.
II. Description of the Prior Art
Mechanical jacks are convenient devices for raising and lowering a portion of a vehicle such as the tongue or forward portion of a trailer. The forward portion may need to be raised or lowered to level the trailer or to position the trailer coupler for connection to the towing vehicle. Typical jacks include telescoping sections, the extension and retraction of which is controlled by an axial screw extending through the housing and drivably engaging a screw nut. Rotation of the screw within the jack may be controlled directly by a crank or through a gear assembly drivably connecting the crank to the screw. Rotation of the crank in one direction rotates the screw causing expansion of the jack sections as the screw nut travels along the screw. Conversely, rotation of the crank in the opposite direction causes contraction of the jack sections as the screw nut travels along the screw in the opposite direction.
The gear drive for the jack includes a first beveled gear mounted to the crankshaft and a second cooperating gear mounted to the axial screw such that rotation of the crank is transmitted to the screw. The cooperation of the components within the jack tube creates difficulty in assembly particularly for components which need to be secured within these limited spaces. In some prior known assemblies the beveled gear would have to be fastened to the crankshaft once assembled within the jack tube. This fastening also reduced the ability to disassemble the gear drive.
The present invention overcomes the disadvantages of the prior known jack assemblies by providing a gear drive which is readily assembled within the jack tube yet has sufficient durability for heavy-duty applications.
The gear drive assembly of the present invention facilitates insertion and assembly of the gear drive components within the limited space of a jack tube without the need for precision insertion of small components such as drive pins. The gear drive assembly is mounted within an upper end of a jack tube and is drivably connected to an axial jack screw extending through the tube. The gear drive assembly of the present invention is driven by a side crank requiring that the rotational motion be transmitted at a right angle. The crank is connected to a crankshaft extending laterally through the jack tube and supported by opposite walls of the tube. The crankshaft includes an intermediate portion having a hexagonal configuration although any non-circular configuration may be employed.
The crankshaft is supported in the opposite walls of the jack tube by bushings which receive the circular end portions of the crankshaft such that the shaft will rotate in the fixed bushings. A first bushing is inserted into the wall of the jack tube from the interior of the tube while the second bushing is inserted into the opposite wall from the exterior to secure the entire drive assembly. A first beveled gear is mounted to the hexagonal portion of the crankshaft. Rotation of the crankshaft is therefore transmitted to the first gear through the hexagonal portion of the shaft. The hexagonal portion has a diameter of the circular end portions and the inner diameter of the bushings thereby preventing the hexagonal portion from moving into the bushings.
The first gear drivably engages a second beveled gear axially aligned with the jack screw whereby rotation of the second gear is transmitted directly to the screw. The second gear is carried on a removable plate extending across the jack tube and connected directly to the jack screw. With the second beveled gear mounted to the screw, the first bushing is inserted into the tube wall from the interior of the jack tube and the first gear is positioned in driving engagement with the second gear with its throughbore aligned with the bushing. The crankshaft is then inserted transversely through the jack tube and the aligned bushing and gear until the hexagonal intermediate portion of the gear is received within the first gear and engages the bushing. The exterior bushing is placed over the end of the crankshaft and fastened to the jack tube to secure the gear drive assembly.
Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawing.